Contact-type slip-rings have been widely used to transmit signals between two members (e.g., a rotor and a stator) that move rotationally relative to one another. Prior art slip-rings of this nature have utilized stator-mounted conductive probes formed of a precious-metal alloy to make contact with a rotating ring. These probes, or sliding contacts, have traditionally been constructed using round-wire, composite materials, button contacts, or multi-filament fiber brushes. The cooperative concentric contact rings of the slip-ring are typically formed to provide a cross-sectional shape appropriate for the probes or sliding contacts. Typical ring shapes have included V-grooves, U-grooves and flat rings. Similar schemes have been used with systems that exhibit relative translational motion, rather than relative rotary motion, and that implement drum-style slip-rings.
When transmitting high-frequency signals through slip-rings, a major factor limiting the transmission rate is distortion of the waveforms due to reflections from impedance discontinuities. Impedance discontinuities can occur throughout the slip-ring wherever different forms of transmission lines interconnect and have different surge impedances. Significant impedance mismatches often occur where transmission lines interconnect a slip-ring to an external interface, at the brush contact structures, and where the transmission lines connect those brush contact structures to their external interfaces. Severe distortion of high-frequency signals can occur from any of these impedance-mismatched transitions of the transmission lines, compounding the distortion with each mismatched interface. Further, severe distortion can also occur due to phasing errors from multiple parallel brush connections and the multipath effects inherent in slip-rings.
The loss of energy through slip-rings increases with frequency due to a variety of effects beyond the normal dielectric and skin effect loses of transmission lines. These effects include circuit resonance, multiple reflections from impedance mismatches, and parasitic inductive and capacitive reactance. These losses are among the key factors that limit high-frequency performance in transmission lines in general, and slip-rings in particular. Because these factors are acute with contact-type slip-rings, other techniques have been explored. High-frequency analog and digital communication across rotary interfaces has also been achieved or proposed by other techniques, such as fiber optic interfaces, capacitive coupling, inductive coupling, and direct transmission of electromagnetic radiation across an intervening space. However, systems employing these techniques tend to be relatively expensive.
What is needed is a contact-type slip-ring module for a slip-ring system that generally addresses the above-referenced problems, while providing a readily producible and economical slip-ring system.